This invention relates generally to chairs which need to be moved sidewise from time to time. An example described here to illustrate one application of the invention is a chair used by a fisherman and mounted on a rear boat seat bench or thwart. For fishing, the chair should be centered for proper balance and to facilitate fishing from both sides of the boat. For operating an outboard motor, however, the fisherman must move to one side so he can reach the motor controls and operates the steering tiller which are centered at the stern.
While comfortable chairs, some complete with tiltable backs, upholstery, and swivel bases, are marketed with clamps for mounting them on boat seat benches or thwarts, they have heretofore been limited to use on forward or intermediate seat benches. Prior to the present invention, such a chair has not been used on the rear seat because, if clamped in the middle for fishing, it would interfere with operating the motor and tiller. No apparatus has been available to readily shift such a chair sidewise between locked center and offcenter positions.